Fluid pressure driving and reversing mechanism



Sept. 12, 1939. l G. F. MAGLOTTl H 2,172,931

'FLUID PRESSURE DRIVING AND REVERSING MECHNISMS l Filed May 29., 1936 4 Sheets-Sheet 1 lll Sept. 12, 1939; G. F. MAGLOTT 2,172,981

` muy) PRESSURE DRIVING AND REVERSING MEGHAN'IsMs v y Filed My 29, 193e l 4 sheets-sheet 2 Sept. 12, 1939. G. F. MAGLOTT FLUID PRESSUREDRIVING AND REVERSING Filed May 29, 19:56

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Sept- 12, 1939. G. F. 'MAGLoTT I 2,172,931

FLUID PRESSURE DRIVING AND REVERSING MECHANISMS Patented Sept. 12, 1939 FLUID PRESSURE DRIVING ANI) REVERS- ING MECHANISM George F. Maglott, Wrenthani,*Massaassigner' .to Brown and SharpeManufacturing Company, a corporation oi' Rhode Island Application May 29, 1936, Serial No. 82,533

9 Claims. (Cl. 12145) The present invention vrelates to improvements in iiuid pressure driving and reversing mechanisms for a reciprocable machine element, and more particularly to a driving and reversing valve mechanism which is well adapted for use in a grinding machine havinga grinding wheel support and a work support, to secure a rapid and smoothly reversing reciprocatory movement of one of said supports relatively to the other.

The invention is herein disclosed as embodiedv in' a preferred form in a hydraulically operated surface grindingmachine comprising with a base, a vertically adjustable grinding wheel support, a longitudinally'reciprocable .work supporting table, and 'a cross slide or saddle on which the table is supported for lateral positioning movements.

It is a principal object of the invention to provide a novel and improved reversing valve mechanism for controlling the supply and exhaustion of liquid under pressure to opposite ends of a cylinder and cooperating piston operatively connected to reciprocate the table, which is well adapted to secure a rapid and uniform deceleration of the table and subsequent acceleration again to driving speed upon reversal with a minimum loss of time in the active loperation of the machine, and without shock or jar.

It is more specifically an object of the invention to providey a valve mechanism of the general description which is well adapted for a sensitive and accurate control of the liquid pressure in each end of the ltable cylinder during the reversal of the table to secure an approximately uniform net retarding pressure and thus a gradually decreasing differential or net operating pressure in the cylinder, and lthereafter a decrease in the net retarding pressure as the table is slowed from driving to zero speed; to .produce a deceleration curve of maximum smoothness and efficiency.

It is another object of the invention to provide a valve mechanism of this general description which will operate as the table stops to produce a graded increase Ain the differential operating pressure suchas to effect an approximately uniform net accelerating pressure on the piston which is substantially maintained until the table is brought up to speed in the opposite 4direction and is thereafter sharply reduced, to secure a similarly eilcient acceleration curve of table movement without shock or jar to the machine.-v

to admit regulated amounts of liquid under pres- I.

sure from the supply simultaneously to both ends. of the table cylinder in order to secure asensitive control of the net decelerating and accelerating y pressures at each stage of the reversal and also in order to provide a yield in the operation of the reversing valve mechanism which will operate to cushion the table against excessive shock or jar.

Another feature of the invention consists in the provision of operating connections in the re, versingv valve which are arranged to permit a throttled re-cireulation of the liquid through theV supply-ports of the reversing valve frogn one end of the cylinder to the other, and thereby to produce a controlled resistance tocontinued table movement during deceleration.

Another feature of the invention consists in the construction and arrangement of the reversing valve which causes regulated decreasing amounts of liquid to be admitted under driving pressure to the exhaust sideofthe cylinder andcooperating piston during the early stages of acceleration to driving speed, and thereby to se- ,cure a smooth and substantially uniform ac-l celeration of the table.

Another feature of the invention col-ists in the provision in the reversing mechanism described, of a throttle device which is rendered operative as the table reaches its desired driving speed, to partially close the exhaust port from the cylinder, and thereby to prevent over-acceleration of the table. Y Y

The several features of the invention consist also in the devices, combinations and arrangement of parts, which together with `the advantages obtained thereby will. be readily understood b`y one skilled inthe art from the following description taken in connection with the accompanying drawings, in -which Fig. 1 is a sectional view in front elevation, of a surface grinding machine, only so much of the Amaehinelceing shown as is believed necessary to illustrate the connection of the present invention therewith; Fig. 2 is a detail sectional view in right side elevation,

' of a portion of themachine illustrating particuvview illustrating particularlyl the hydraulic driving connections for the work supporting table; Figs. 4 to 9 inclusive, are a series of sectional views illustrating successive steps in the operation of the reversing valve to reverse the. direction of table movement; Fig. 10 is a view .Similar to Figs. 4 to 9 inclusive, illustrating the valve in dead center position during reversal;

Fig. 11 is a chart in which the areas of valve openings from each end of the table driving cylinder both to pressure and exhaust are plottedv for each step in the movement of the reversing valve from one operating position to the other; and Fig. 12 is a diagrammatic view illustrating an alternative arrangement of the hydraulic connections shown in Fig. 3, in which a smooth table reversal is effected by re-circulation of the exhaust fluid, the pressure and exhaust connections to the reversing valve having been reversed.

Referring specifically to the drawings, the base of the surface grinder illustrated is generally indicated at 26 in Fig. 1, a grinding wheel at 22, and a vertically adjustable supporting column for the grinding wheel at 24. The machine is also provided with a longitudinally reciprocable work table 26 slidably supported on a saddle or cross slide member 28 which is in turn carried on cross ways 36 and 32 on the base 26.

Reciprocatory movements are imparted to the table by means of hydraulically operated connections which include a cylinder 34 secured to the saddle member 28 and a cooperating piston 36 which is connected to move with the table by means of a piston rod 38 extending through a packing box 46 in one end of the cylinder, and connected at one end to the piston 3 6 and at its other end to a downwardly extending lug 42 formed at the right hand end of the table. The construction and mode of operation of the hydraulic system employed for reciprocating the table 26, will be readily understood in connection with.the somewhat diagrammatic Fig. 3 of the drawings. The pressure medium, preferably oil, is drawn from a reservoir or sump 44 in the base of the machine by means of an oil pressure pump 46, and is carried through a pressure supply line 48 and extension 56 thereof, to a table throttle valve 52 which compriseswith the casing 52 a rotatable throttle valve member 54 having formed therein an irregular aperture 56 through which oil under pressure is admitted to a pipe connection 58 and the reversing .valve 66. The table reversing valve comprises with the cylindrical casing 664 therefor, an axially shiftable valve member 62 having portions thereof cut away, as hereinafter more fully set forth, to form a central oil pressure supplychamber 64 and two exhaust chambers 66 and 68 upon opposite sides thereof. Two pipe connections 16 and12 connect the reversing valve respectively with the two ends of the table cylinder 34. With the reversing valve in its runningposition to the extreme left as shown in Fig. 3, oil under pressure is admitted from the table throttle valve through the chamber 64 and pipe connectionA 16 to the left hand end of the tabl'e cylinder 34, while at the same time oil is exhausted from the righthand end oi' the cylinder through the pipe con-l nection 12, the chamber 66 in the'reversing valve, and an exhaust connection 14 from which the exhausted liquid passes through the exhaust line 'I6 of the system through a low pressure check valve 16 to the sump 44 in the base. Similarly, when the table reversing valve member 62 is moved to its .running position to the extreme right, oil under pressure passes from the table throttle valve 52 through the pressure supply chamber 64 in the reversing valve and pipe connection 12 to the right hand end of the table cylinder 34, oil being exhausted at the same time from the left hand end of the cylinder 34 through the pipe connection 16, the chamber 66 in the reversing valve 66, and an exhaust connection 86 therefrom to the 4exhaust line 16 and reser voir 44.

In order to maintain a substantially constant available driving pressure in the system, there is provided in the supply line 46 adjacent the pump 46, a high pressure relief valve 62. For purposes of illustration it may be assumed that the relief valve 82 is set to maintain a driving pressure of substantially 100 lbs. per square inch in the system, and that the relief valve 16 in the exhaust line is adjusted to maintain an exhaust back pressure of about-4 lbs. per squar inch.

In the preferred embodiment of the invention disclosed,'the movable valve member 62 of the reversing valve 66 is shifted from one to the other of its alternative operating positions through the operation of hydraulically operating means which operates to produce a positive and uniform rate of travel of the valve member 62 from one operating position to the other. Thev connections through which the position of the reversing valve member 62 is controlled, comprise a pilot valve .96,in the form of a cylinder having mounted therein an axially movable valve member 82. Liquid under pressure is admitted to a pressure chamber 64 formed by a central spool portion of the pilot valve member $2 by wa'y of a throttle 66 and connections 66 from the supply line 48, and passes through a pipe connection |66 to the right hand end of the reversing valve 66, or alternatively through a pipe l connection |62 to the left hand end of the reversing valve 66. With the pilot valve member 92 in the position shown in Fig. 3, liquid under pressure has been admitted through the chamber 94 and connection |66 to the right hand end of the reversing valve 66, so that the reversing valve member 62 is moved to its extrme position to the left at a rate which is determined by the size of the throttle `66. Liquid has simultaneously been exhausted from the left hand end of the reversing valve 66 through the pipe connection |62 and an exhaust chamber |64 in the pilot valve member 62, and thence through an exhaust connection |66 to the main exhaust line 16. Conversely, when the pilot valve 92 is moved to the left, the connection 62 to the left hand end of the reversing valve 66 is connected with the pressure chamber 64 and throttle opening 66, and the pipe connection |66 to the right hand end of the cylinder is connected through an exhaust chamber |66 in the pilot valve member 62 and exhaust connection ||6 to the main exhaust line 16, so that the reversing valve member 62 is moved in a reverse direction to the rightA again at a constant rate of speed which is determined by the throttle opening 66.

The position ofthe pilot valve member 62 is conveniently controlled either manually or by the operation of table dogs through connections (see Figs. 2 and 3) comprising a valve stem ||2 secured toone end of the pilot valve member 62 and having a pin and slot connection with a lever arm 4 secured to the lower end of a vertically extending post ||6supported on the'saddle member 26. lTo the upper end of the post 6 there is secured a. control lever |16 vwhich is formed to permit convenient manipulation by the operator, and is provided witha rearwardlyY extending projection arranged to extend into the path of actuating dogs lll'adjustably mounted ,divani l Y 3 inaT-shapedslot |22int'liefxontsidcofthe table 2l.

In accordance with the present invention. applicant's reversing valve mechanism is constructed and arranged so that the movement of the reversing valve member I! from one operating position to the other will operate to regulate the eifectlve decelerating or braking pressures set up in the table cylinder 84 in accordance with lo the rate of deceleration and actual table speed at each successive instant during .the-slowing of the table from driving to zero speeds, and thereafter to secure a. similarly regulated control of the net accelerating or driving pressure in the table cylinder during the acceleration oi the table again from aero to dri in the opposite directies Applicant is aware that attempts have been made te secure a graduated deceleration in the speed of the moving support by diminishing in varying ratio the areas oi the pressure and exhaust ports to the two ends offs. driving cylinder ,c and pistou. The regulation of the decelerating pressures secured in this manner is compara- '.5 tively irl-elastic. and if not adjusted exactly to the rate of movement oi' the table at each moment during the deceleration thereof, will Inaccordance with a principal feature 4of the present invention, the reversing valvey member A '$2 is constructed and arranged with relation to aa'the supplyand-exhaust connections Il and 12 to each end of the table cylinder 1I, to admit increasing amounts of liquid under pressure from the supply line lIl and throttle valve '52 to the exhausting end of the cylinder 3l while the con-9 40 nection therefrom to the exhaus'tline 18 is gradually shut olf, so that the stopping of the table is eifected against an always yielding pressure, the maximum value of which is determined after the supply connection to the exhausting end oi' 45` the cylinder starts to open by the areas of the throttled port openings and by the resisting pressure in the supply line 4l as determined by the setting of the relief valve '32, and is therefore v to a considerable extent independent of ,the rate ..0 of movement ci' thev table at any given linstant during the deceleration, and the corresponding areas of the supply and exhaust ports to the table cylinder 34 at that instant. As thev re- Y versing valve approaches itscentral Position, and.

principle of operation ofthe reversing valve inwhich deceleration and the subsequent acceleration of the table in opposite directions are con- Ii trolled by the simultaneous admission of varying amounts oi liquid under pressure to both ends of the table cylinder Il, it hasbeen found possible to secure a graduated control of the net braking pressures in the table cylinder il,

I0 in which the braking pressure is maintained at a high level as the table speed is cut down, land thereafter again decreases as the table approaches nero speed to produce a deceleration curve of maximum eillciency.

i5 In order to secure a maximum application of 'increase in vthergrcss retarding pressure.

braking premure during the middle portion of the decelerating period, gradually increasing amoimts of fluid pressure medium are admitted to the exhausting sideA of the cylinder at the same time that the exhaust line is gradually 6 shut oil', thus producing a rapid but controlled As, shown in Fig. "l, additional liquid forced out of the exhausting side of the cylinder 3l by the pressure set up by the momentum of the table 10 is nowvre-circulated to the feeding end of the cylinder through the supply chamber 6I against the supply pressure and against an additional resistance provided by the throttling of the ports from the reversing valve chamber 6 to the pipe 15 connections 10 and l2. As the table deceleration approaches zero speed, the continued movement of the valve member 62 will have completely shut off the exhaust connection from the port |34 to the exhaust port IM as shown in Fig. l0. 2@ At the same time, however, the port opening from the pressure chamber t@ to the port i313 is increased, allowing a comparatively free re-cir'- sure of table momentum, through the port i363, g5 pressure chamber Il and port .|36 to the other side? of the driving cylinder 3l and piston 36,

so. that the gross deceleratlngl pressure is reduced at the exact moment when this is most desirable, that Vis to say, when the table `apa0 preaches zero speed.V l.

A continued movement of the valve member I! past center position further increases the pressure valve opening through port IM, and at the same time further reduces the pressure valve kopening through port |36, again restricting the re-circulation between the two ends of the driving cylinder and building up a relatively greater pressure through' the port |34 tothe left hand end of the driving cylinder. With this arrange- 40 ment of the reversing valve, it will readily be seen that the actual stopping of the table takes place against a yielding cushion provided by the supply` pressure which has a known value determined by the setting of the pressure relief valve l2. Inasmuch as liquidv under pressure is still being supplied -to the pressure sideof the table cylinder 1l, the net braking pressure` at the point of actual reversal maybe maintained at the constant theoretical value or is preferably even reduced to insure the gradual stopping of the table without shock or Jar.

Further in Aaccordance. withthe present inven- A. tion, the reversing valve mechanismv is arranged toproduce a smooth and substantially uniform v' acceleration of the `table from zero to'drlving .speed in the opposite direction. To this end the supply of liquid under pressure to the now exhaustlng side of the table cylinder 34, is not completely shut ol! until after the table has begun to 6o move in a reverse direction. The corresponding l exhaust valve opens causing the gross accelerating pressure to be set ata maximum value, thus maintaining amt-accelerating pressure as nearly constant 'as possible until the table is brought 65 up to speed. being then sharply reduced,.to produce a similarly efficient acceleration curve of table movement to exactly. the desired driving speed in-the opposite direction. v Y( The construction and mode of .operation of. ap- 70 plicants improved reversing valve for the attainment of the above-stated objects, will be readily understoodffrom Fig. 3, and the some- -whatdiagrammatic views Figs. 4 to ,l0 inclusive. As shown in'these ilgures. the barrel portions 75 |26 and |28 of the valve member 62 adjacent the pressure supply chamber 64, are tapered as indiycated respectively at |30 and |32 to permit a gradual throttling or vopening of the cooperating ports |34 and |36 in the valve casing 63 con-.

nected respectively to the pipe lines 16 and 12. In order to permit throttlingv the ow of the exhausted liquid from the table cylinder 34 through A'haust chamber 66, or alternatively through the pipe connection 12 and port |36to.the exhaust chamber 68, to taper |33 is formed in the barrel portion |26 of the valve member 62 adjacent the exhaust chamber 66, and a similar taper |40 is provided in the end of the barrel portion |23 adjacent the exhaust chamber 63. There is also provided at the outer or left hand end of the exhaust chamber 66, a land |42 which is arranged as the reversing valve member 62 reaches its extreme operating position to the right, and as the table is brought up to full driving speed, to partially shut oil? the flow of exhaust fluid from the chamber 66 through the exhaust port |44 in the valve casing to the exhaust line 16. Similarly,there is provided at the outer or right hand end ofthe exhaust chamber 63, a land |46 which is arranged as the reversing valve member 62 reaches its extreme operating position to the left illustrated in Fig. 3, to partially shut off the ow of liquid from the exhaust chamber 63 through the cooperating exhaust port |43.

The operation of the reversing valve to reverse the direction of travel of the table, will be readily understood from the somewhat diagrammatic views Figs. 4 to 10 inclusive, taken in connection with Fig. 11, which illustrates in chart form the variations in the eiective port areas through which liquid is admitted unde pressure from the pressure chamber 64 to each end of the cylinder 34 through the ports |34 and |36, and similarly the effective areas of the openings through which y liquid is exhausted from each end of the cylinder represent area of valve opening. i Lines |34P and |36P represent the variations in the areas of the valve openings to the ports |34 and |36 through 'which liquid under pressure is admitted to each end of the cylinder 34 at different stages in the movement of the reversing valve member 62 from one to the other of its alternate driving positions. Similarly, the lines |34E and |36E represent the variations in area oi the exhaust valve openings from ports |34 andy |36 through which` liquid is exhausted from each end of the cylinder 34 to th' exhaust chambers 66 and 63 of the reversing valve during the movement of the reversing valve member 62 from one position to the other.

Fig. 4 of the drawings illustrates the valve in its position to the extreme right, or opposite to that shown in Fig. 43, in which liquid under pressure is being supplied freely to the right hand end of the table cylinder 34 through the port |36 and supply line 12, and liquid is being exhausted from the left hand end of the cylinder 34 through the pipe connection 10 and port |34 to the exhaust chamber 66 from which it passes through For purposes of illustrathe exhaust port |44 and connection 30 to the exhaust line 16.V This position corresponds to that indicated at 4 in Fig. 11. Assuming that the table pilot valve 30 is now rendered operative to move the reversing valve member 62 to the left to reverse the direction of movement of the table, it will be seen froman inspection of the chart in Fig. 11, that the valve will move slightly more than l, of an'inch before any appreciable retard of the table begins. Fig. 5 of the drawings shows this condition, in which the area of the port opening l|36P from the pressure chamber 64 has been slightly reduced, a `somewhat greater reduction having taken place in the port opennig |34E to the exhaust chamber 66, thus producing a relatively small retardlng force, and slightly reducing the rate of movement of the table. When the valve 62 has been moved to the station illustrated by Fig. 6, it will be seen that liquid has begun to flow from the pressure chamber 64 through the port |34, thus admitting a small amount of liquid under pressure to the exhausting end of the cylinder 34. The area of the passageway |36P from the pressure chamber 64 to the port |36 has been still further decreased, and a still further reduction has taken place in the area of the exhaust opening from the port |34 to the exhaust chamber 66. These changes inthe valve openings have had the effect of considerably increasing the retardlng pressures in the table cylinder 34, and thus increasing the rate of deceleration of the table. Continued movement of the valve member 62 to4 the position shown in Fig. 7, and as illustrated by the chart Fig. 11, causes the area o f the valve opening |36P from the pressure chamber 64 through the port |36 to be still further reduced, the exhaust opening |34E to the exhaust chamber 66 through the port |34 to be reduced even more drastically somewhat less than one-third of its original size, while at the same time the area of the opening |34P from the pressure chamber 64 through the port |34 to the left hand end of the table cylinder 34 has been increased, so that the retardlng effect is now to a considerable extent due to the resistance set up by the reduction in the driving pressure due to the admission of liquid under pressure to the exhausting or left hand side of the table cylinder 34ethrough the port |34P. The area |34E is, however, still considerably greater than the area |34P, so that most of the return liquid goes to exhaust.

Dur'ing the time when the valve member 62 passes through positions illustrated by Figs. 10 and 8 respectively, a new stage in the operation of retarding the table movement is introduced, the exhaust connection |34E has closed oif entirely, and the pressure throttle connections |36P and |34P to the pressure chamber 64 of the reversing valve are nearly equal. Also, as the reversing valve member 62 passes the exact cen- 4ter position shown in Fig. 10, the exhaust connection designated asl36E starts to open. At this time practically all the liquid lowing to and from the table cylinder 34 is being re-circulated through the central portion oi.' the reversing valve comprising the pressure chamber 64 and the throttle pressure ports |34P and |36P. The retarding effect at this time is produced principally by the resistance to the passage of the liquid from one end of the table cylinder to the other through the throttle ports |34P and |36P. The table has now slowed to nearly zero speed, and the net retardlng pressure has at the same ,l 2,172,981 time dropped, thus preventing any possibility of' ignated as |34P has opened to a considerable extent, and the opening to the exhaust from the vright hand side -of the cylinderA represented as INE has increased. It will be noted that the;` next accelerating pressure provided by the opening of the pressure port |34P and exhaust port I 36E is controlled by the still open throttle at |36P which operates tof-prevent any sudden urge in the building up of the accelerating pressure, with a consequent shock or jar to the machine. As the pressure port |361 .is completely shut on and the pressure port |34l? and exhaust port HSE continue to open, the accelerating pressure of the table is maintained ata maximum until the full speed operation of the table is attained. In order to avoid over-acceleration as the table reaches its full operating speed to the right and after port |34P has reached its full opening, the land |66 operates to partially close or throttle the exhaust port |48 from the exhaust chamber 68, thus introducing a secondary resistance in the exhaust side of the cylinder 34 and bringing to an abrupt stop further acceleration. of the table which now continues to move at a uniform rate of speed under the full control of the main throttle 52 of the machine.

While the valve mechanism constructed and arranged `to operate as above set forth, consti- Atutes a. preferred embodiment of the invention, -it will be understood that certain features of the invention are applicable more broadly-to other types and constructions of .reversing valve mechanisms within the scope and spirit of the'appended'claims. The value of the connections illustrated for producing the re-circulation of the pressure medium betweenthe two ends of the driving cylinder and ram, is not -limited to the speelde embodiment illustrated, since a similarly effective control in the stopping and reversing ofthe table can be obtained by a throttled re-clrculation ofthe exhaust fluid which is independent ofthe pressure line connections. Such a construction, for example, might comprise an arrangement in which the pipe line 58 is connected to exhaust and the lines 14 and 80.

to pressure, so'that the effect is produced by the re-circulation of the exhaust rather than the pressure Huid. This arrangement is specifically illustrated in Fig. 12 of the drawings, in which the conduits I4 and Il' are connected to the pressure supply line 48, so that fluid under pressure is supplied to each of the valve ports |48 and |44, and the pipe connection 58 to the central portion or the reversing va1ve so,

together with the throttle valve 54' and conduit 50' are connected directly with the exhaust line 16. The mechanical construction shown in this gure, is otherwise identical with that shown in Fig. 3. Withthe modified construction shown in Fig. 12, a re-circulation of the exhausting fluid under pressure caused by the table momentum, is allowed to take place through the chamber $4 between the two ends of the cylinder 34 for a restricted central portion of movement of the reversing valve member, the tapered portions and |32 providing a throttled passageway of increasing and thereafter decreasing area for the controlled .re-circulation of the fluid medium.

'Ihe operation of the reversing valve the modified connections shown in Fig. 12, may

be briefly set forth in connection with Figs. 4 to 8 inclusive, showing successive positions of the valve member. Referring to Figures 4, 5 and 6, it will b e seen that successive throttling of the pressure liquid occurs at port |34, co-acting with tapered portion |38, and that it occurs earlier than in the former case where pressure was in chamber 84; but without the application of pressure on the reverseport- |36.

Figures 6 and 7' show. the rapid reduction of pressure in |34 by by-passing it'into'chamber tt. Somewhere between positions shown in lig- 4ures 7 vand 8, rse-circulation from the two endsv of the cylinders takes place via the heavily throttled ports iME and |36E, with practically no driving force in throttled port |341. Up to this point, it willbe Vnoticed that. retard is accomplished more by reducing the driving'orceV than by increasing the force on the reverse side of the piston (via port |36E); the net or differential pressure eiect 'beingr much the same as formerly.

in Fig. 8, however, pressure is actively brought to bear on port |36, thus increasing the retarding force. Note that ports |36 and |34 are still by-passed and rei-circulating, with only exhausty pressure on port |34, giving something less than this value on the driving facel 'of the piston, by virtue of the resistance at lport |34.-

At, `or slightly after the position shown in Fig.'

9, reversal takes place, with vpressure building up markedly in portV |36, and only exhaust through port |34. lReversal will occur slightly later than in the former case, the action being4 quite shockless or soft; acceleration, corrspondingly.- will be more rapid. The result, however,

is quite an acceptable reversal, laccomplished' without undue waste of time.

The invention having been described, what is claimed is:

1. In a fluid pressure actuated driving and r'esource from which a :duid medium issupplicd vata predetermined pressure, of a reversing, valve having a port connected to each end of the cylinder and having a valve member movable between alternative operative positions for controlling admission and exhaust of the pressure medium to and from each end of the cylinder through said ports, said valve member having fluid exhaust chambers including throttle connections cooperating with said ports during movement of the valve member from one operating position to the other to gradually shut oil the exhaust connection to` one of said ports and thereafter to gradually open the exhaust connection vto the other of said ports, and a fluid pressureV supply chamber in said valve member including throttle connections to each of 'said ports arranged during movement. ofthe valve member from one operating position to the other lgradually to'close one throttle opening; and at the same time to gradually open the other throttle openingl and thereby to permit a controlled recirculation of fluid through said supply chamber a predetermined pressure, of a reversing valve having a port connected to each end of the cylinder and having a valve member movable between alternative operative positions for controlling admission and exhaust of the pressure medium to and from each end of the cylinder through said ports. said valve member having uid exhaust chambers including throttle connections cooperating with said ports during movement of the valve member from one operating position to the other to gradually shut ofi the exhaust connection to one of said ports and thereafter to gradually open the exhaust connection to the other of said ports, a fluid pressure supply chamber in said valve member including throttle connections to each of said ports arranged during movement of the valve member from one operating position to the other gradually to close one throttle opening, and at the same time to gradually open the other throttle opening and hereby to permit a controlled recirculation of fluid through said supply chamber from one end of the cylinder to the other, and means for moving said valve member from one to the other of said positions at a predetermined uniform rate.

3. In a fluid pressure driving ad reversing mechanism for a reciprocable support, the combination with a cylinder and piston operatively connected to drive the support, and a source from which a fluid pressure medium is supplied under pressure, of a valve device including a movable valve member for controlling admission and exhaust of the uid pressure medium to and from thevends of the cylinder, said valve device having throttle connections operable upon movement of the valve member from one operating position to the other to gradually reduce the exhaust of pressure medium from one end of the cylinder to substantially zero for an intermediate position of said valve member, andthereafter gradually to open the other end of said cyinder to exhaust, and additional throttle connections operative during the movement of said valve member from one operative position to the other to gradually shut off the flow of fluid pressure medium to the latter end of the cylinder, and while iiuid pressure medium is still being supplied to said latter end of the cylinder, to admit slowly increasing amounts of said pressure medium tothe rstmentioned end of said cylinder, a connection between said latter throttle connections to permit a controlled re-circulation of the uid pressure medium as the valve member passes through its intermediate position, and means for moving sa'id valve member from one to the other of said positions at a predetermined uniform rate, the varia-v tions in area of said throttle connections being related to the distance travelled by said valve member to maintain a substantially uniform net retarding pressure to slow the support, then to eiect a rapid reduction of the net retarding pressure as the support approaches zero speed so `that reversal takes place after the valve member passes middle position, and thereafter to maintain a substantially uniformA net accelerating pressure to accelerate the support.

4. In a fluid pressure actuated driving and reversing mechanism for a reciprocable support, the combination with a cylinder and piston operatively connected to drive the support, and a source from which a uid pressure medium ls supplied at a predetermined pressure, of a valve device including a movable valve member for controlling admission and exhaust of the fluid pressure medium to and from the ends of the cylinder, said valve device having means operable during movement of the valve member from one operating position to the other to gradually shut oil? the exhaust from one end of the cylinder and thereafter to gradually open the exhaust to the other end of the cylinder, and additional means operative during the movement of said member from one operating position to the other to gradually shut oi the flow of fluid pressure medium to the latter end of the cylinder and at the same time to admit gradually increasing amounts of fluid pressure medium from the source to the first-mentioned end of the cylinder, and means rendered operative as the support is brought up to speed, in an opposite direction, to again partially close the exhaust from said latter end of the cylinder.

5. In a fluid pressure actuated driving and reversing mechanism for a reciprocable support, the combination with a cylinder and piston operatively connected to drive the support, and a source from which a fluid pressure medium is supplied at a predetermined pressure, of a valve device including a movable valve member for controlling admission and exhaust of the fluid pressure medium to and from the ends of the cylinder, said valve device having means operable during movement of the valve member from one operating position to the other to gradually shut off the exhaust from one end of the cylinder and thereafter to gradually open the exhaust to the other end of the cylinder, and additional means operative during the movement of said member from one operating position to the other to gradually shut off the flow of fluid pressure medium to the latter end of the cylinder and at the same time to admit gradually increasing amounts of fluid pressure medium from the source to the firstmentioned end of the cylinder, means rendered operative as the support is brought up to speed, in an opposite direction, to again partially close the exhaust from said latter end of the cylinder, and means for moving said valve member from one to the other of said positions at a predetermined uniform rate.

6. In a uid pressure driving and reversing mechanism including a cooperating driving cylinder and piston through which a fluid medium under pressure is supplied for reciprocating a support, a reversing valve comprising a body having an inner cylindrical surface, a fluid pressure supply port and spaced at each side thereof, outlet ports connecting respectively with opposite ends of the driving cylinder, and beyond these, additional ports through which the respective ends of the driving cylinder are connec. :d to exhaust, and a valve member movable between alternative limiting positions within said body having a central reduced or spool portion to provide a pressure supply chamber connecting with said supply port,

and at each side of said supply chamber additional Y.

jacent exhaust chambers to provide throttle connections respectively with said outlet ports shaped to fully shut ofi each of said connections to exhaust upon movement of said valve member to said central position.

7. In a fluid pressure driving and reversing mechanism including a cooperating driving cylinder and piston through which a uid medium under pressure is supplied for reciprocating a support, a reversing valve comprising a body havling an inner cylindrical surface, a iiuid pressure 'supply por't, and, spaced at each side thereof, outlet ports connecting respectively with opposite ends ofthe driving cylinder, and beyond these,

additional'ports through which the respective ends of the driving cylinder are connected to exhaust and a valve member movable between alternati've limiting positions within said body hav-` ing, a central reduced or spool portion to provide a pressure supply chamber connecting with said supply port, at each side of said' supply chamber additional spool portions to provide exhaust chambers for connecting each end of said driving cylinder to exhaust, and barrel portions interposed between said chambers having the ends thereof tapered to provide throttle connections from each of said outlet ports respectively to the pressure supply chamber and the adjoining exhaust chamber, and additional barrel vportions spaced lengthwise of said valve body and connecting respectively with opposite ends of said driving cylinder, a port intermediate said outlet ports connected to exhaust, and a pair of ports spaced beyond said outlet ports towards opposite ends of the valve body connected to supply, and a y valve member movable between alternative limiting positions within said body having a central spool portion and at each side thereof additional spool portions separated by barrel portions tapered toward the central spool portion to providea throttled .inter-connection between said outlet ports and the intermediate port 4for a restricted central portion of movement of the valve member whereby a controlled re-circulation of the uid medium from one end of the cylinder tothe other is permitted under the pressure caused by support momentum, said barrel portions being vtapered also toward the other spool portions to provide a throttle connection respectively between said outlet ports and the adjacent port of said pair arranged with the valve body in a central portion to substantially shut oiI both of said pair of ports from the adjacent outlet ports, and means for moving said valvemember from one to the other of said limiting positions at a predetermined uniform rate, the variations in area of the throttle connections provided by said tapered portions being related to the distance travelled by the valve member to maintain a substantially uniform net retarding pressure to slow the support, then to eilect a rapid reduction of the net retarding pressure as the support approaches zero speed so that reversal takes place after the valve member passes middle position, and thereafter to maintain a substantially uniform net accelerating pressure to accelerate the support.

9. In a fluid pressure driving and reversing mechanism for a reciprocable support, the combination with-a cylinder and piston operatively connected to drive the support and a source from which a pressure medium is supplied, of a-valve device including a valve member movable between alternative operating positions for controlling admission and exhaust of the fluid pressure medium to and from each end of said cylinder, said valve device having throttle connections operable during movement of the valve member from one operating position to the other for gradually shutting oil' the pressure connection to one end of the cylinder and for opening the pressure connection `to the other end of thev cylinder, and similarly for shutting ofi, and for opening the exhaust connections to opposite ends of said cylinder, the variations in area of said throttle connections being related to the distance travelled by said valve member to maintain a sub-v stantially uniform net retarding pressure to slow the support, and thereafter a substantially uniform net accelerating pressure to accelerate the support, a connection between the throttle con-7 nections to opposite ends of the cylinder operable as the valve member approaches a central position, to provide a throttledi connection of increasing area, and as the valve member leaves said central position, of decreasing area for the rex-circulation of the fluid medium under pressure caused by the support momentum directly between the ends of the cylinder for effecting a rapid reduction of the net retarding pressure as the support approaches zero speed that reversal `takes place after the valve member passes middle position, and means for moving said valve member from one to the other of said operating positions at a predetermined uniform rate. I

GEORGE F. MAGLOTI. 

